1. Field of the Invention
The present invention relates to a maintenance method and a maintenance apparatus for an ink jet head that ejects ink droplets onto recording paper for printing characters and graphics.
2. Description of the Related Art
Generally, an ink jet printer is equipped with an ink jet head where a plurality of ink jet nozzles are arranged. The ink jet head easily gets to a state where it is difficult to eject ink because the nozzle is clogged or a pressure loss occurs due to paper dust or an air bubble entering through an orifice arranged at the tip of each ink jet nozzle. Therefore, maintenance of the ink jet head is required for recovery from the state to overcome this problem.
For example, Jpn. Pat. Appln. KOKAI Publication No. 5-517 discloses an ink jet printer that performs such maintenance. This ink jet printer attaches a cap closely to head nozzles and operates an ink suction pump with an atmosphere valve closed to generate a negative pressure in the cap and suck an air bubble or dirt in the nozzles. In the middle of this suction process, the ink jet printer further opens the atmosphere valve and once returns the air bubble remaining in the nozzle to the ink. The ink jet printer again closes the atmosphere valve and sucks the ink to completely eject the air bubble.
If the atmosphere valve is opened in the middle of the suction process to once return the air bubble remaining in the nozzle to the ink as mentioned above, however, a dirt particle such as paper dust attached to the nozzle also enters the nozzle. There has been a problem in that the dirt particle, depending on its size or shape, cannot be ejected even if the atmosphere valve is closed again to suck the ink.